A method of the above-described kind is known from EP-A-289 849. In it the paste is stirred with the use of driven stirring tools in the paste chambers. The amount of cooling medium flowing through the cooling chambers is so increased that a turbulent streaming condition results. During a contact-free removal of the mass from the cooling or heating surfaces by means of the stirring tools a shear rate in the line between the cooling or heating surface on the one hand and the stirring tools on the other is used.
The cooling medium continuously streams through the cooling chambers of one or more cooling stories and is conveyed in big amounts through each circulation. Cold water is supplied in a controlled manner to the circulation via a valve, a regulator being applied which is controlled by a probe measuring the temperature of the mass. The cooling medium is guided through the cooling story in reverse direction. By means of this guidance of the cooling medium in cooperation with the substantially increased amount of throughput of cooling water, the disadvantages of an on/off switch of a solenoid valve in a supply line for cold water are avoided. It is however still necessary to regulate the temperature of the cooling medium at the input into the last cooling story facing the heating story in order to meet differing mass throughput amounts and/or mass input temperatures. By way of this the temperature of the cooling surfaces changes depending on the control condition especially in the end area of the last cooling story. The control is so designed that at the end of the last cooling step, i.e. at the transfer into the subsequent heating step, the mass to be tempered shows a substantially constant temperature. A substantially constant mass temperature at the end of the last cooling story is however not equal to a constant portion of crystals in the mass.
DD-PS 136 570 shows a method and a device for continuously tempering chocolate paste with a tempering machine having a cooling story, a dwell story and a subsequent heating story. Each of the three stories is equipped with its own cooling or heating circulation, the cooling chambers or heating chambers are streamed through in parallel flow to the mass chambers. In order to influence the type and size of the forming crystals and in order to temper a chocolate paste in such a way that it is in a state of equilibrium at processing temperature, the paste is successively conveyed through the three stories. The three stories of the tempering machine are formed of about the same size, however, the conveying organ in the area of the second tempering story is altered in comparison to the corresponding areas of the other stories by an enlarged cross section and/or increase in length. In the first story the chocolate paste is cooled off to a certain temperature which is lower than the processing temperature and higher than the critical equilibrium temperature of the instable crystals. This story is the only cooling story. Unstable crystals supposedly cannot form in this cooling story. In the second story, the dwell story, there is no cooling, but the chocolate paste is held in continuous throughput over a comparatively longer period of time at a constant temperature. The constant temperature guide in the dwell story takes place by temperature regulation on the side of the cooling water, so that it is not the temperature of the cooling surface which is kept constant but the temperature of the chocolate paste. This way the chocolate paste is to be transferred into a thermodynamic condition of equilibrium in which a sufficient number of crystals is to form. In the third story, the heating story, the chocolate paste is heated up to processing temperature, here again the temperature being adjusted to the chocolate paste in such a manner that temperature fluctuations of the chocolate paste are avoided if possible. The publication does not contain solutions for solving the problems caused by fluctuating mass throughput and/or changing mass income temperatures.
A further known tempering machine works with a tempering column which is equipped with two cooling stories and one heating story. Each of the two cooling stories is allocated a cooling circulation equipped with a pump; also, a heating circulation driven by a pump is provided for the heating story. Here too the cooling medium is guided in reverse direction through each story. The circulation of the cooling medium and of the heating medium is increased so that a turbulent streaming condition is created. The mass to be tempered is conveyed through the tempering machine with the aid of a pump. In turbulent mixing and in continuous scraping of the cooling surfaces the mass emits or absorbs heat. At the end of each story a probe is provided which measures the temperature of the mass and each triggers a regulator which controls a valve in the cold water supply of the corresponding cooling or heating circulation. The pumps at each circulation of each story continuously circulate the cooling or heating medium. The temperature of the cooling medium automatically adjusts to the cooling needs. By way of this temperature change of the cooling water in dependence of the mass throughput and the mass income temperature, the temperature of the cooling surfaces, especially at the end side of the last cooling story facing the heating story, fluctuates greatly or within wide limits which is not useful for the precrystallization. This results in varying viscosities in the mass to be tempered, and primarily varying portions of stable .beta.-crystals, even though, the temperature of the mass fluctuates within comparatively narrow limits at the end of the last cooling story and hence also at the end of the heating story.